The prior art of motor-powered depilatory devices using springs for removing skin hair is based on a well-known operational concept of an early mechanical device disclosed in Swiss Pat. 268,696 to Fischer. This han-operated device uses an arched coil spring to trap hair between its loops as it rolls over the skin. The rolling motion of the coil spring traps hairs in the spaces between the spring loops on the convex side and plucks them when these spaces close on the concave side. Hairs are trapped about one-half of the spring diameter away from the skin, so that short hairs "escape" and are not plucked.
Several tweezer designs are disclosed in the group including Swiss Patent 179,261 to Macioce, U.S. Pat. No. 2,458,911 to Kerr, U.S. Pat. No. 2,486,616 to Schubiger, British Patent 203,970 to Davis, U.S. Pat. No. 1,743,590 to Binz, and U.S. Pat. No. 1,232,617 to Shipp. All are coil spring designs which vary in the mechanical arrangements for stretching the spring and engaging the hair between coil spring loops before it is trapped upon closure of the stretched spring. Because they are based on manual operation, these designs are inherently limited in their efficiency, so that they cannot be directly compared with motorized versions of hair removal devices. In addition, the coil spring provides only limited contact area with individual hairs, and may cause "tearing" rather than plucking of hair, thus limiting efficiency.
U.S. Pat. No. 4,079,741 to Daar et al. discloses a single tension spring arranged to be stretched and compressed so as to pluck hairs trapped between its loops. The spring is arranged parallel to the skin and is stretched once during each revolution of a cam, causing friction with the skin and making the operation inefficient. The overall design is complicated an expensive.
An arched helical spring provided with high speed rotational motion for opening and closing the loops is provided in U.S. Pat. No. 4,524,772 to Daar et al. Upon detailed inspection, it is seen that the contact between the helical spring and individual hairs is point-like, so that the hair may be pinched and not plucked. Also, rotation of the helical spring causes transverse deflection of hair, so that shorter hairs are not trapped due to lateral movement of the spaces between the loops. U.S. Pat. Nos. 4,726,375 and 4,807,624 to Gross et al. disclose a rubber hairplucking element with partially circumferential slits or rubber discs for trapping and plucking skin hair.
These patents are all based on the concept of rotating the coil spring or slits near the skin to enable hairs to become trapped, but they create friction with the skin which causes an unpleasant sensation of heat while consuming excessive motor power during use. The tendency of these spring and rubber elements to "wind" while slowly developing sufficient hair-pulling tension creates additional discomfort in use of these devices. Because friction is generated with the skin, extra motor power is required, and this is problematic where size restrictions exist for the device.
U.S. Pat. No. 1,923,415 to Bingham discloses a plurality of rotatable discs arranged to be bent one or more times toward each other at a point during each revolution, causing them to pluck bird feathers. This design generates friction with the skin, is inefficient, complicated and expensive to manufacture.
Another device for removing bird feathers is disclosed in French Patent 1,123,971 to Jadoul, based on a plurality of rotatable discs arranged to be bent toward one another at a point during each revolution, again, causing friction and inefficiency.
French Patent 1,017,490 to Bachofen discloses another bird feather plucking device using a set of rotatable discs, each disc having a curved surface area, and being arranged to be bent toward one another at a point during each revolution. Again, friction and inefficiency are disadvantages of the device.
Another poultry feather plucking device is disclosed in U.S. Pat. No. 2,496,223 to Lanzisera, based on the use of a helical spring which rotates on one side of a grid, such that feathers which project through the grid are grasped between loops of the spring and are plucked. This design allows only one plucking action per revolution of the spring, and causes friction, besides being complicated and expensive to manufacture.
In U.S. Pat. No. 4,575,902 to Alazet, there is disclosed a depilatory device comprising a series of adjacent, closely-spaced hair-plucking discs driven by an electric motor. The discs are periodically deformed during rotation so as to trap hair between them as they are pressed together. This design is inefficient since the discs close only once per rotation, limiting plucking action to a short time interval.
A design similar to Alazet is marketed by Calor under the tradename "Caresse" and uses two cam-operated shafts for moving a set of movable tweezers againt a set of fixed discs in one direction only, once per revolution. Another similar design is marketed by Braun under the tradename "Silkappeal" and has a plurality of moving segments closing against one another once per revolution. Both are complicated and inefficient designs.
Another disc design is disclosed in U.S. Pat No. 2,900,661 to Schnell, wherein a pair of discs rotate at a large angle to each other and converge at a contact point whereat hairs are plucked. The large size of this design makes it inefficient, and the inflexible discs tend to cut the hair, not pluck it.
In French Patent 2,637,784 to Demeester et al., there is disclosed a rotary head having a set of tweezer blades which operate to open and close to pluck hairs at least once during rotation. The design is complicated, expensive, and inefficient.
In all of the previous designs, the friction generated with the skin generates heat and causes an unpleasant sensation. In addition, the area over which the hair removal device is effective is determined by the size of the plucking element, which limits the number of hairs which can be simultaneously plucked within this area.
In my previous U.S. Pat. No. 4,935,024 there is disclosed a novel coupled-disc element which reduces the "winding" phenomenon of previous designs, while reducing the painful sensation.
It would therefore be desirable to provide a power-driven depilatory device which provides efficient hair removal over a widened skin area while reducing friction with the skin.
It would also be desirable to provide a depilatory device which is simple in construction for cost-effective production, while durable in use.
Additionally, it would be desirable to provide a depilatory device which minimizes pain and is simple to use and maintain.